As shown by the prior art patents below referenced, there has been a substantial amount of work done toward protecting electronic components in hot, deep well bores. Various coolants have been proposed and used as well as both liquid and solid eutectic materials. These materials are normally termed "heat sinks" or heat sponges which purpose is to absorb the heat generated both internally from the electronics and externally from transmission of heat from the well bore through the side walls of the logging apparatus. Materials with high specific heat are commonly used. Also, solid materials having appropriate melting temperatures are utilized to take advantage of their heat of fusion.
The vacuum or "Dewar" flask has been extensively used in downhole tools, often in combination with heat sink devices as mentioned above.
The environment encountered in well bores reaches elevated temperatures which are considerable in deep wells and in certain geographical locations. Temperatures approaching 600.degree. F. are encountered. Present efforts are to provide electronic components which will operate satisfactorily in temperatures up to 400.degree. F., at least for a limited time period of operation. Generally the lower temperature at which electronic components can be maintained during well bore operations than the longer and more reliable are the operation of such components.
Scintillation detection devices, which employ scintillation crystals coupled to a photomultipler tube or device will deteriorate rapidly to an inoperative state at elevated temperatures much lower than the usual electronic components.
The electronic components are desirably maintained in a dry gaseous environment such as air or nitrogen since the insulation and wiring of such components are susceptible to leaching by any sort of liquid, such as refrigerant, which in turn can lead to component failure.
Presently known prior art patents relating to this invention are as follows: U.S. Pat. Nos. 2,469,461, 2,561,738, 3,038,075, 3,187,824, 3,254,221, 3,321,625, 3,435,629, 3,521,063, 3,654,470, 3,714,981, 4,056,949, 4,107,937, 4,120,353, 4,169,387, 4,407,136, 4,480,186, 4,485,670.